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Ask any Republican  from the Speaker of the House to a local sheriff  what the biggest problem facing the country is today and you're sure to get the same answer: Debt. Conservatives believe a public debt of $14 trillion and growing is crippling the economy and condemning future generations to penury. In Wisconsin, new Republican governor Scott Walker says that a $137 million deficit leaves him no choice but to force public unions in the state to accept drastic benefits reductions and curtailed bargaining rights  a stance that has brought tens of thousands of protesters to the streets of Madison. In Congress, the Republican-controlled House has passed a budget that would slash $60 billion in government spending, most of it from discretionary programs. "We're broke," Speaker John Boehner told Meet the Press last week. "It's time to get serious about how we're spending the nation's money."

It's not that President Barack Obama and the Democrats don't talk about the danger of spiraling public debt. Obama's own fiscal 2012 budget included a five-year freeze on nonsecurity discretionary spending. But when it comes to serious slash-and-burn deficit reductions  and alarming rhetoric about what unchecked public debt will do to the country  Obama just can't compete with his friends across the aisle. "We face a crushing burden of debt," Wisconsin Republican Paul Ryan said in his response to last month's State of the Union speech. "The debt will soon eclipse our entire economy, and grow to catastrophic levels in the years ahead." (See "Paying for Nature.")

Now, I'm not a political reporter  thankfully  but I've heard that sort of rhetoric before, this warning that we're living beyond our means, running up a tremendous debt that will one day cause catastrophe. It's the call of the environmentalist, and it was on display just a few blocks away from the Capitol in Washington this weekend at the annual summit of the American Association for the Advancement of Science. Speaker after speaker took the podium in stuffy halls around the Walter E. Washington Convention Center to warn that we had exceeded the planet's carrying capacity  with too many people, too much pollution and too much carbon dioxide  and that unless we cut back drastically on consumption, our world would collapse, and us with it. "Right now we're living at about 1.5 planets' worth of consumption," says Jason Clay, senior vice president for market transformation at the World Wildlife Fund. "We are living beyond what is sustainable. That can't go on forever."

Even the terms we use to describe our two debts are similar, as the language used in finance bleeds over into ecology. Conservationists like to talk about "natural capital"  the stuff provided by the planet that underpins prosperity. Clean air, clean water, soil, forests, fish, biodiversity  this is the natural capital in our balance sheet, and without it there would be no life, let alone business. One study done in the mid-1990s estimated that the total value of such ecosystem services was approximately $33 trillion  considerably more than the global GDP at the time. The business of the planet is the environment. (See why foodies can save the green movement.)

If we act sustainably  if we live within our means, as conservatives might put it  our natural capital will regenerate and sustain us, like a bank account delivering interest. But we're not living within our means  not even close. Just to take one example from the conference, Villy Christensen of the University of British Columbia (UBC) Fisheries Centre looked at global fish stocks and found that big predatory fish like tuna and cod have declined by more than two-thirds over the past century. Fifty-four percent of that decline has taken place over the past 40 years, when factory-fishing boats began sweeping the oceans. Christensen explained the dramatic disappearance of our favorite fish in terms that might be familiar to any budget hawk. "You can think of the fish biomass as our capital in the bank," he said. "We can draw an interest from that capital every year. But we have been eroding the capital year after year, and we are now left with so small fish stocks that the world catches are smaller now than they were in the 1980s."

Admittedly, there are economists who argue that these fears are overblown, that humanity has been able to keep growing through technological innovation that has multiplied the carrying capacity of the planet. There were doomsayers in the 1970s who predicted imminent global starvation; instead, we've thrived economically, pulling hundreds of millions of human beings out of poverty. That's exactly how most conservatives talk about the natural debt, if they talk about it all. We'll keep growing, keep innovating our way out of anything nature throws in our path. And if that doesn't work, there's always divine intervention. "God is not capricious," Minnesota Republican Mike Beard said recently. "He's given us a creation that is dynamically stable. We are not going to run out of anything." (See 51 ways to save the environment.)

But the truly scary possibility is that the collapse could come quite suddenly, after what may seem to be a long period of global prosperity. It would only be in retrospect, after the fall, that we would see that what we thought was success was built on eating into our capital, like a consumer maxing out his credit cards to buy a second house. The global rise in food prices, which have hit their highest level globally in several decades, might be an early sign that the agricultural system that sustains (some more than others) nearly 7 billion people with the help of fertilizers and irrigation may be hitting its limits. "When the crisis hits, we'll act rapidly, but by then it might be too late for hundreds of millions or even billions of people," says William Rees, an ecologist at UBC.

What's amazing to me, though, is that the very politicians who are so worried about the public debt  and who want deep spending cuts now to save our future, whatever the cost  utterly dismiss the idea that we could face an equal crisis of natural debt. Politicians like Boehner and Ryan order us to tighten our belts immediately, but they utterly deny the climate and resource crisis the world faces. In fact, the Republicans in Congress are going well beyond simple denial  they're now using their budget to erode America's ability to prepare for that very scary future.

The Republican budget would cut the Environmental Protection Agency (EPA) budget by one-third  $3 billion  and would prevent the agency from setting any limits on CO2 and a number of other pollutants. It would eliminate U.S. funding for the Intergovernmental Panel on Climate Change  which would save all of $12.5 million. It would cut Department of Energy budgets that promoted renewable energy by $1.7 billion  a 23% reduction at a time when the U.S. is in a clean-energy race with China. The National Science Foundation budget would be cut by $395.5 million. "This is probably the single most irresponsible bill I have seen either Chamber of Congress pass in the more than 20 years I have been in Washington," wrote Dan Lashof, the director of the Natural Resource Defense Council's climate center.

To which the Republicans would respond, We face an unprecedented fiscal crisis, and tough choices have to be made. All right  but if you believe public debt is such a potential catastrophe that it must be defused now, no matter the short-term pain, it only seems right to take our natural debt just as seriously. Either way, we're broke  and it's time we acted like it.